Load compensated control system



July 20, 1943. w. H. GILLE arm. 2,324,692

LOAD COMPENSATED CONTROL SYSTEM Filed April 14, 1941 TEMPERATURE REbPONSH/E RESISTANCE I w so so :10: so so /93 13 E g I7 54 1H 55 i r f i0 r B6 r Ff r" I! J INVENTORS Willi. H-Gillc. John. V. Sigiord. BY A M m ATTQRNEY Patented July 20, 1943 LOAD COMPENSATED CONTROL SYSTEM I Willis H, Gille, St. Paul, -Minn., and John V.

Sigiord, Wabash, Ind., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minm, a corporation of Delaware Application April 14, 1941, Serial No. 388,368 (Cl. 236-74) 8 Glaims.

This invention relates to proportioning control systems in general, and has for an object to improve that type'oi proportioning control system wherein means is provided to change the setting of the system in response to a change in the system load.

changing the condition value maintained by the control system. Other objects and advantages will become ap- 7 parent to those skilled in the art upon reference to the accompanying specification, claims and drawing, in which:

The single figure diagrammatically discloses a follow-up control system embodying the load compensating mechanism of our invention. Certain features essential to our invention are shown on an enlarged scale, while other features of conventional construction are reduced.

The drawing shows a furnace l having a burner H which is supplied with fuel through a conduit 12 controlled by a valve [3. Heated fluid is carried from the furnace III through a pipe H to a heating system including a radiator ii. In the radiator IS the fluid gives up its heat to the space in which the radiator is located and the spent fluid then returns to the furnace l0 through a pipe l5.

The valve I3 is operated by a stem on which is mounted a rack 2|. The rack 2| is driven by a pinion 22 operated by a motor generally indicated at 23 through a gear train schematically shown at 24. The motor 23 has a pair of windings 25 and 26 which operate the motor in opposite directions.

Energization of the windings 25 and 26 is controlled by a switch arm 30 moving between opposed stationary contacts 3i and 32. The switch arm 30 is mounted on the moving coil 33 of a galvanometer generally indicated at 34. The galvanometer 34 is connected to a bridge circuit having input terminals 4| and 42 and output terminals 43 and 44. Three of the arms of the bridge circuit consist of fixed resistances 45, 45

and 41. Between the arms 45 and 46 of the bridge is connected a slide wire resistance 55 across which a sliding contact 5| is moved. The sliding contact 5| is shown as rigidly attached to the stem 20 o! the valve l3 Ior movement therewith. It should be noted that output terminal 44 of the bridge is the point at which contact 5i engages the resistance 50. The fourth arm of the bridge includes a temperature responsive resistance 52 located in the space heated by the radiator 15, and two rheostats 53 and 54.

The portion of the resistance 54 which is con- 'nected in series with the temperature responsive resistance 52 is controlled by a movable switch arm 55 driven by a reversible motor generally indicated at 55 through a gear train schematically shown'at 51. The motor 56 is provided with a pair of windings ill and SI which operate the motor in opposite directions. The energization of these windings is controlled by a switch arm 52- which moves between opposed stationary contacts 63 and 54. on and operated by a temperature sensitive bimetallic element 65 which is exposed to the temperature of the space being heated by the radiator i5.

The bimetallic element 55 is flxedat the end opposite the contact arm 82 to a plate member 66 which is pivotally mounted as at 51 on a panel 88 in the space heated by the radiator 15. The temperature responsive resistance element 52 and the rheostat 53 are also mounted on the panel '68. A lever 10 is pivotally mounted as at II on the panel 68 and has a portion 12 projecting below the lower edge of the panel 68. An indicator pointer I3 is attached to the portion .12 of the lever Ill and cooperates with a scale I4 on the panel 58 to indicate the temperature which the system is set to maintain. An arm 15 is fixed to the lever III in any suitable manner and serves to vary the portion of rheostat 53 which L is connected in series with the temperature responsive resistance 52, in accordance with the temperature setting of the system as determined by the position of the lever ID. The lever Ill also has an arm 16 extending toward the plate member 66 and having a suitable connection, as, for example, a pin and slot connection, with the plate member, as indicated at ll.

The motors 56 and 23 are supplied with energy from a transformer "having a primary winding 8i and a secondary winding 82. The bridge circuit 40 is supplied with energy by a battery 82 connected to the input terminals 4| and 42.

The switch arm 82 is mounted Operation With the parts in the position shown in the drawing, the system has been set to maintain the space temperature at 70, and the space temperature is at that value, as indicated by the fact that the switch arm 62 is engaging neither of the contacts 63 and 64. The operation of the system will first be considered as though the switch arm 62, and the rheostat 54 operated thereby, were omitted. If the temperature of the space being heated now falls below 70 the resistance of the element 52 is decreased. This decrease in the resistance of element 52 decreases the resistance between the terminals 4| and 43 below thairbetween the terminals 4| and 44 of the bridge circuit. This results in an increase of the potential of terminal 43 with respect to that of terminal 44, and a current flows from terminal 43 through a conductor 85, movable coil 33 of galvanometer 34, and a conductor 84 to output terminal 44. The passage of this current through the movable coil 33 causes a deflection of the coil such as to move switch arm 30 into engagement with contact 3|. This completes an energizing circuit for winding 25 of motor 23. This circuit may be traced from the left hand end of transformer secondary winding 82 through a conductor 86, a conductor 81, switch arm 30, contact 3|, a conductor 88, winding 25, a conductor 89, to the right hand end of transformer secondary winding 82.

Energization of winding 25 causes motor 23 to be driven in such a direction as to open the valve l3 wider and move the sliding contact 5| upwardalong the resistance so as to decrease the resistance between terminals 4| and 44 of the bridge circuit 40.

As soon as the resistance between terminals 4| and 44 of the bridge has been decreased by an amount corresponding to the decrease in resistanceof the temperature responsive resistance 52, the output terminals 43 and 44 come to the same potential, and current ceases to flow through galvanometer coil 33. The switch arm 30 thereupon moves away from the contact 3| to its neutral position and the motor 23 stops.

If the temperature in the space being heated increases, the resistance of the element 52 would increase with'the result that a current would flow from terminal 44 to terminal 43 of the bridge circuit, thus passing through coil 33 in an opposite direction to that previously described. This current flowing through the coil 33 causes the switch arm 30 to be operated against the stationary contact 32. This completes an energizing circuit for the secondary winding 26 of motor 23 which may be traced from the left hand end of secondary winding 82 through conductors B6 and 81, switch arm 30, contact 32, a conductor 90, winding 26 and conductor 89 to the right hand end of secondary winding 82.

Energization of winding 26 causes operation of the motor 23 in such a direction as to drive the valve l3 towards closed position and to move the sliding contact 5| downward along the resistor 50 so as to increase the resistance between terminals 4| and 44. When this resistance has increased sufliciently to balance the increase in resistance of element 52, the current ceases to flow through coil 33, and the motor stops.

The motor 56 and the energizing circuit therefor controlled bythe switch arm 62 constitute a means for compensating the control system for the amount of load thereon, the operation of which will now be discussed. When the temperature in the space being heated falls below the desired value, the bimetal element 65 moves the switch arm 62 against contact 63. This complete's an energizing circuit for winding 60 of motor 56 which may be traced from the left hand end of secondary winding 82 through conductor 86, plate member 66, bimetal element 65, switch arm 62, contact 63, a conductor 9|, winding 68, and a conductor 92, to the right hand end of secondary winding 82.

Energization of winding 60 causes the motor 56 to drive the sliding contact arm 55 over the rheostat 54 in such a direction as to decrease the amount of resistance included in the bridge circuit. The motor 56 and the gear train 51 are designed to move the switch arm 55 very slowly, for example, one degree in thirty minutes. Since switch arm 62 remains in engagement with contact 63 as long as the temperature of the space stays below the value which the system is set to maintain, it will be seen that the motor 56 continues to slowly reset the position of slider 55 along resistance 54.

The object of this control system is to operate the valve |3 to a position such that the heat input from the radiator l5 to the space being heated is the same as the heat which is being lost from the space. If the space temperature decreases, it is indicative of the fact that heat is being lost from the space at a greater rate that it is being supplied to thespaceby the radiator I5. The purpose of the load compensating mechanism including the motor 56 and the rheostat 54 is to introduce into the bridge circuit a resistance which will cause a permanent resetting of the position of valve I3 at which the bridge circuit 40 is balanced. The amount by which the valve is reset will be proportional to the direction and duration of a deviation of the space temperature from desired value. The-effect of such a resetting on the valve I3 is to change the heat input to the space heated bytthe radiator I5 by an amount sufiicient to makeup for the increased heat loss sired value, which has been indicated as 70, the

contact arm 62 would be moved away from contact 63 by the action of the bimetallic element 65,

.thereby deenergizing the winding 60 of the fnotor 66 and terminating the resetting effect of the motor 56 on the contact arm 55. The rise in temperature would, at the same time, increase the resistance of element 52, thereby unbalancing the bridge circuit 40, so as to cause motor 23 to drive the valve |3 to a closed position. When the'valve stem 20 is moved downwardly far enough to rebalance the bridge circuit through the action of sliding contact 5| on the resistance wire 58, the bridge will be rebalanced. The final valve position will differ from the original valve position by an amount proportional to the movement of slider 55 along resistance 54.

The function of the load compensating mechanism is to reset the valve position to a value such that the heat input by the radiator l5 exactly equals the heat lost from the space. The function of the temperature responsive element 52, on the other hand, is to change the valve setting temporarily by a sufficient amount to cause the heat input to be changed sufliciently to return the space temperature rapidly to its desired value. As the return of the space temperature to the desired value is accomplished, the effect due to the temperature responsive element 52 is to move the valve in the opposite direction, back towards its original position. The operation of the motor 56 in driving the switch arm 55 over the resists: is moved against the right'hand contact a, thereby energizing the motor, winding 5| through the circuit previously described. The motor 561 ance 54, however, has caused a change in the resistance of the bridge net work which is not re-- moved by the return of the space temperature to its original position. The valve l3 therefore stops at a diiierent position than it was before the temperature decrease took place. The space temperature is again at 70 but the heat input to the furnace l and hence the heat input to the space through the radiator l5 has been increased by an amount sufiicient to take care of the increased heat loss which caused the original decrease in temperature.

When the temperature of the space increases above the desired value, the operation of the load compensating mechanism is similar to that previously discussed. In this case the increase in temperature will cause the bimetallic element 55 tomove contact arm 62 against stationary contact- 64. This completes a circuit which may be traced from the left hand end of secondary wind- "ing 82 through conductor 85, plate member 55, bimetallic element 55, switch arm 62, contact 64,

value of the space temperature which the system is to maintain. This means comprises the extension 12 on the lever arm which may be moved along the scale 14 to any desired temperature reading on the scale. shown as manually movable, it will be readily understood by those skilled in the art that a clock This will cause a permanent resetting of the therefore drivesthe contact arm 55 in a, direction to increase the portion or resistance 54 in the bridge circuit and therefore compensates to some tem temperature is reachedthe valve I3 remains set at its new position to which it wa moved through the action of the rheostat 53.

ily occur to those skilledin the art.

While the lever 10 is,

or other conventional automatic means might be used.

Suppose now that the lever arm ID has been moved to the left so that the indicator 13 is op which is in series with the temperature responsive element 52. This will cause a permanent resetting of the position of valve IS in accordance with the new resistance value between the terminals 4| and 43 in the same manner as the increase in resistance 54 caused a permanent resetting of the valve l3 towards closed position. This will decrease the supply of fuel to the burner II and will therefore decrease the heat supply to the space by the radiator 15. s

The temperature of the space will not of course fall at once to the new desired value, but will slowly drop. This decrease in temperature results in a decrease in resistance of element 52,

and hence in an unbalanceof the bridge circuit such as to cause movement of the valve towards open position. This action is however balanced to some extent by the load compensating mechanlsm.

When the lever 10 is moved to set the system temperature at the plate member 66 is moved by the action of the pin and slot connection 11 so that the temperature at which the switch arm changed to 60. The temperature at the time of this change in setting being 70, the switch arm It the rheostat 53 were not" used, the only way or cha'ngingthe system temperature wouldbe to change the setting or the bimetallic element 55,

and then wait for the slow operation of the load compensating motor 55 to drivethe contact arm, 55 over the'resistance 54 by an amount sufiicient tochange the temperature setting of the system torits new desired value. Because of the ex- 'tremely slow operation of the load compensating motor 55 the adjustment of the system temperature obtained by such a method would be unwieldy'and impractical.

The resistance 53 theretore provides a quick method oiadiusting the system temperature.

Other modifications of our invention will read- For instance, other types of bridge circuits might be readily used, or means for amplifying the output of the bridge circuit might be used. Such an amplifier might eitherbe of the electronic type or of the type which intermittently clamps the galvanometer pointer and then operates a mechanism so that one of two or more switches 'is selectively closed, depending upon thepointer position. Our invention is not therefore limited to the simple embodiment disclosed herein but is defined by the appended claims,

We claim as our invention:

1. Incombination, a device to be positioned in a plurality orfpositions for controlling the value of a conditionja bridgecircuit including an elesaid condition, means resp nsive to the unbalance of said bridge circuit for sitioning said device and rebalancing said bridge, a first adjustable impedance in said bridge circuit'for changing the value of said condition maintained by the device,

ment whose resistivity MES in accordance with an adjustable compensating impedance connected in said bridgecircuit, means responsive to the deviation of said condition from a predetermined value'for adjusting said compensating impedance, and'means for simultaneously adjustmg, said first impedance and said deviation responsive means.

2. In combination, a device to be positioned in a plurality of positions ior controlling the value .of a condition, a bridge circuit including an eleable impedance in said bridge circuit for changiiig the value of said condition maintained by the device, an adjustable compensating impedance connected in said bridge circuit, means responsive to a condition indicative of the load on said device for adjusting said compensating impedance, and means for simultaneously adjusting 52 engages neither of the contacts 53 and 54 is said first impedance and said condition responsive means.

3. A system for maintaining a condition at a predetermined value, comprising in combination, a device to be positionedin a plurality ofpositions for controlling the value of a condition, an

electric circuit including a first resistance, whose resistivity varies in accordance with said condition, means responsive to the flow of current in said circuit for positioning said device, a second resistance adjustable in magnitude and connected in series with said first resistance, a third resistance adjustable in magnitude and connected in series with said first resistance, means responsive to a deviation of said condition from its predetermined value for adjusting said second resistance, manually operable means for adjusting said third resistance and thereby changing the magnitude of said predetermined value, and an operative connection between said manually opcrable means and said deviation responsive means whereby said deviation responsive means is adjusted simultaneously with said third resistance so as to operate upon a deviation of the condition from the value determined by said third resistance.

4. A system for controlling the temperature of a space, comprising in combination, temperature changing means, a device to be positioned in a plurality of positions for controlling said temperature changing means, a bridge circuit including a resistance element with an appreciable temperature coefiicient of resistance, an adjustable resistance element connected in said bridge circuit, means including a thermostat responsive to a deviation of said space temperature from a predetermined value for adjusting said last mentioned resistance, a second adjustable resistance element connected in said bridge circuit, means foradjusting said second resistance and simultaneously changing the setting of said thermostat, and means responsive to the unbalance of said bridge circuit for changing the position oi said device.

5. A system for controlling the temperature of a space, comprising in combination, temperature changing means, a device to be positioned in a plurailty of positions for controlling said temperature changing means, a bridge circuit including a resistance element with an appreciable temperature coefiicient of resistance, an adjustable resistance element connected in said bridge circuit, a reversible electric motor, double-throw switch means controlling the energization and rotational direction of said motor, adjustable driven by said motor for adjusting said last Inentioned resistance, a second adjustable resistance element connected in sai ge circuit, means for simultaneously adjusting said second resistance lement andsaid thermostat, and means responsive to the unbalance of said bridge circuit for changing the position of said device.

6. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, a bridge circuit including an element Whose resistivity varies in accordance with a condition indicative of the need for operation of said device, means responsive to the unbalance of said circuit for positioning said device and rebalancing said circuit, a first adjustable impedance in said circuit for changing the value of said controlled condition, an adjustable compensating impedance connected in said circuit, means responsive to the deviation of said controlled condition from a predetermined value for adjusting said compensating impedance, and means for simultaneously adjusting said first adustable impedance and said deviation responsive means.

7. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, a normally balanced electrical circuit including impedance means variable in response to a condition indicative of the need for operation of said device, means responsive to the unbalance of said circuit for positioning said device and rebalancing said circuit, a first ad'- justable impedance in said circuit for changing the value-of said controlled condition, an adjustable compensating impedance connected in said circuit, means responsive to the deviation of said controlled condition from a predetermined value for adjusting said compensating impedance, and means for simultaneously adjusting said first adjustable impedance and said deviation responsive means.

8. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, means for modulatingly positioning said device, normally balanced control means for said positioning means, means responsive to changes in a condition indicative of the need for operation of said device for producing an unbalancing efiect in said control means, means operated by said positioning means for opposing said unbalancing effect and rebalancing said control means, first means for varying the relationship between said unbaiancing and rebalancing effects in response to deviations of said controlled condition from a predetermined value, second means for varying said relationship manually, and means associated with said second means and ope'fated simultaneously therewith to change said predetermined value by an amount corresponding to the change in said relationship.

1 WILLIS H. GILLE. JOHN V. SIGF'ORD. 

